In some AIMD systems such as commercially available cochlear implant systems, Spinal Cord Stimulator (SCS) systems, all of the data communications and power supply requirements are met via a close transcutaneous arrangement with an external transmission coil placed on the skin directly over the implanted receiver coil such as described, for example, in U.S. Patent Publication 2012/0109256, which is incorporated herein by reference in its entirety. In other types of AIMD systems such as Implantable Cardiac Defibrillators (ICD) and Heart Pacemakers (PM) have primary galvanic cells as power source and for telemetry purposes use either a coil arrangement as described above, or else an RF link in the Medical Implant Communication Service (MICS) frequency band (402 to 405 MHz) that requires a separate IC and a matched antenna (coil). For the sole purpose of data transfer, MICS transceivers are more compact than an inductive coil system and these devices work at a distance of up to 2 m and so can be utilized in the surgical operating theatre. A major task is to keep the power consumption of the device small so that the overall lifetime of an implant with a primary cell is not significantly reduced.
In AIMD systems that use an inductive communication coil arrangement, telemetry data from the implanted components back across the skin to the outside is typically performed using load modulation of the receiver coil arrangement to modulate the load on the external transmitter coil. That requires the external coil to be in close vicinity to the implanted coil, which during implantation surgery can only be achieved if the external coil is placed in a sterile package and is then positioned close to the open surgical wound. That limits the freedom of the physician/surgeon to manipulate the implant, e.g. optimizing the implant or electrode position while the implant is operating.
One typical example of an AIMD system is a cochlear implant. A normal ear transmits sounds as shown in FIG. 1 through the outer ear 101 to the tympanic membrane (eardrum) 102, which moves the bones of the middle ear 103, which in turn vibrate the oval window and round window openings of the cochlea 104. The cochlea 104 is a long narrow duct wound spirally about its axis for approximately two and a half turns. The cochlea 104 includes an upper channel known as the scala vestibuli and a lower channel known as the scala tympani, which are connected by the cochlear duct. The scala tympani forms an upright spiraling cone with a center called the modiolar where the spiral ganglion cells of the acoustic nerve 113 reside. In response to received sounds transmitted by the middle ear 103, the fluid filled cochlea 104 functions as a transducer to generate electric pulses that are transmitted to the cochlear nerve 113, and ultimately to the brain. Hearing is impaired when there are problems in the ability to transduce external sounds into meaningful action potentials along the neural substrate of the cochlea 104.
In some cases of hearing impairment, a cochlear implant AIMD system may be provided that electrically stimulates auditory nerve tissue with small currents delivered by multiple electrode contacts distributed along an implant electrode. FIG. 1 shows some components of a typical cochlear implant system where an external microphone provides an audio signal input to an external signal processor 111 which implements one of various known signal processing schemes. The processed signal is converted by the external signal processor 111 into a digital data format, such as a sequence of data frames, for transmission by an external transmitter coil 107 across the skin into a receiver processor in a stimulator processor 108. The stimulator processor 108 extracts the audio information in the received signal and also a power component that provides electrical power for the implanted parts of the system. The receiver processor in the stimulator processor 108 may perform additional signal processing such as error correction, pulse formation, etc., and produces a stimulation pattern (based on the extracted audio information) that is sent through connected wires 109 to an implant electrode 110. Typically, the implant electrode 110 includes multiple electrodes 112 on its surface that provide selective stimulation of the cochlea 104.